We conduct a comprehensive numerical study of the orbital dependence of harassment on early-type dwarfs consisting of 168 different orbits within a realistic, Virgo-like cluster, varying in ...eccentricity and pericentre distance. We find harassment is only effective at stripping stars or truncating their stellar discs for orbits that enter deep into the cluster core. Comparing to the orbital distribution in cosmological simulations, we find that the majority of the orbits (more than three quarters) result in no stellar mass loss. We also study the effects on the radial profiles of the globular cluster systems of early-type dwarfs. We find these are significantly altered only if harassment is very strong. This suggests that perhaps most early-type dwarfs in clusters such as Virgo have not suffered any tidal stripping of stars or globular clusters due to harassment, as these components are safely embedded deep within their dark matter halo. We demonstrate that this result is actually consistent with an earlier study of harassment of dwarf galaxies, despite the apparent contradiction. Those few dwarf models that do suffer stellar stripping are found out to the virial radius of the cluster at redshift = 0, which mixes them in with less strongly harassed galaxies. However when placed on phase-space diagrams, strongly harassed galaxies are found offset to lower velocities compared to weakly harassed galaxies. This remains true in a cosmological simulation, even when haloes have a wide range of masses and concentrations. Thus phase-space diagrams may be a useful tool for determining the relative likelihood that galaxies have been strongly or weakly harassed.
ABSTRACT We study the intrinsic shapes of a sample of over 400 quiescent galaxies in the cores of the Virgo and Fornax clusters with luminosities 106 ≤ Lg/L⊙ ≤ 108. Similar to satellites of the Local ...Group and Centaurus A, these faint, low surface brightness cluster galaxies are best described as a family of thick (〈C/A〉 > 0.5), oblate-triaxial spheroids. However, the large sample size allows us to show that the flattening of their stellar distribution depends both on luminosity and on the presence of a nuclear star cluster. Nucleated satellites are thicker at all luminosities compared to their non-nucleated counterparts, and fainter galaxies are systematically thicker as well, regardless of nucleation. Once nucleation is accounted for, we find no evidence that the environment the satellites live in plays a relevant role in setting their 3D structure. We interpret both the presence of stellar nuclei and the associated thicker shapes as the result of preferential early and rapid formation, effectively making these faint nucleated galaxies the first generation of cluster satellites.
The dynamics of globular cluster systems (GCSs) around galaxies are often used to assess the total enclosed mass, and even to constrain the dark matter distribution. The GCS of a galaxy is typically ...assumed to be in dynamical equilibrium within the potential of the host galaxy. However cluster galaxies are subjected to a rapidly evolving and, at times, violently destructive tidal field. We investigate the impact of the harassment on the dynamics of GCs surrounding early-type cluster dwarfs, using numerical simulations. We find that the dynamical behaviour of the GCS is strongly influenced by the fraction of bound dark matter f
DM remaining in the galaxy. Only when f
DM falls to ∼15 per cent do stars and GCs begin to be stripped. Still the observed GC velocity dispersion can be used to measure the true enclosed mass to within a factor of 2, even when f
DM falls as low as ∼3 per cent. This is possible partly because unbound GCs quickly separate from the galaxy body. However even the distribution of bound GCs may spatially expand by a factor of 2-3. Once f
DM falls into the <3 per cent regime, the galaxy is close to complete disruption, and GCS dynamics can no longer be used to reliably estimate the enclosed mass. In this regime, the remaining bound GCS may spatially expand by a factor of 4 to 8. It may be possible to test if a galaxy is in this regime by measuring the dynamics of the stellar disc. We demonstrate that if a stellar disc is rotationally supported, it is likely that a galaxy has sufficient dark matter that the dynamics of the GCS can be used to reliably estimate the enclosed mass.
An analysis of ages, metallicities, and a/Fe ratios of globular cluster systems in early-type galaxies is presented, based on Lick index measurements summarized in Puzia et al. (2004, A&A, 415, 123, ...Paper I of this series). In the light of calibration and measurement uncertainties, age-metallicity degeneracy, and the relative dynamic range of Lick indices, as well as systematics introduced by abundance ratio variations (in particular variations of a/Fe ratios), we find that the most reliable age indicator for our dataset is a combination of the Lick Balmer-line indices HgA, Hb, and HdA. MgFe' is used as a spectroscopic metallicity indicator which is least affected by a/Fe variations. We introduce an interpolation routine to simultaneously derive ages, metallicities, and a/Fe ratios from diagnostic grids constructed from Lick indices. From a comparison of high-quality data with SSP model predictions, we find that 62/3 of the globular clusters in early-type galaxies are older than 10 Gyr, up to 1/3 have ages in the range 65-10 Gyr, and only a few cluster are younger than 65 Gyr. Our sample of globular clusters covers metallicities from Z/H - -1.3 up to 60.5 dex. We find that metal-rich globular clusters show on average a smaller mean age and a larger age scatter than their metal-poor counterparts. a/Fe diagnostic plots show that globular cluster systems in early-type galaxies have super-solar a/Fe abundance ratios with a mean a/Fe = 0.47 c 0.06 dex and a dispersion of 60.3 dex. We find evidence for a correlation between a/Fe and metallicity, in the sense that more metal-rich clusters exhibit lower a-element enhancements. A discussion of systematics related to the Lick index system shows that the method suffers to some extent from uncertainties due to unknown horizontal branch morphologies at high metallicities. However, these systematics still allow us to make good qualitative statements. A detailed investigation of indices as a function of data quality reveals that the scatter in Balmer index values decreases for higher-quality data. In particular, extremely low Balmer index values that are lower than any SSP model prediction tend to disappear. Furthermore, we find that observed photometric colors are in good agreement with computed SSP colors using ages and metallicities as derived from the spectroscopic line indices.
We present spectroscopic ages, metallicities, and α/Fe ratios for 70 globular clusters in M 31 that were derived from Lick line-index measurements. A new interpolation technique of age-metallicity ...and α/Fe-diagnostic grids is used to account for changes in index strength as a response to abundance-ratio variations, in particular for all of the Balmer-line Lick indices. In addition to a population of old (>10 Gyr) globular clusters with a wide range of metallicities, from about -2.0 dex to solar values, we find evidence for a population of intermediate-age globular clusters with ages between ~5 and 8 Gyr and a mean metallicity Z/H ≈ -0.6. We also confirm the presence of young M 31 globular clusters that were recently identified by Beasley et al. (2004, AJ, 128, 1623), which have ages $\la$1 Gyr and relatively high metallicities around -0.4 dex. The M 31 globular cluster system has a clearly super-solar mean α/Fe = 0.14 ± 0.04 dex. Intermediate-age and young objects show roughly solar abundance ratios. We find evidence for an age- α/Fe relation in the sense that younger clusters have smaller mean α/Fe ratios. From a comparison of indices, mostly sensitive to carbon and/or nitrogen abundance, with SSP model predictions for nitrogen-enhanced stellar populations, we find a dichotomy in nitrogen enhancement between young and old M 31 globular clusters. The indices of objects older than 5 Gyr are consistent with a factor of three or higher in nitrogen enhancement compared to their younger counterparts. Using kinematical data from Morrison et al. (2004, ApJ, 603, 87) we find that the globular cluster sub-population with halo kinematics is old ($\ga$9 Gyr), has a bimodal metallicity distribution, and super-solar α/Fe . Disk globular clusters have a wider range of ages, are on average more metal-rich, and have a slightly smaller mean α/Fe ratio. A cross-correlation of structural parameters for M 31 globular clusters with spectroscopically derived ages, metallicities, and α/Fe ratios shows a correlation between half-light/tidal radius and metallicity, which is most likely due to the correlation of half-light/tidal radius and galactocentric distance. We compare our results for M 31 globular clusters with those obtained with the same technique for globular clusters in the Milky Way, Large Magellanic Cloud, M 81, and other spiral galaxies in the Sculptor group. Finally, we compare the globular cluster systems of the two Local Group spirals, M 31 and Milky Way, with their integrated bulge light.
We present VLT/F0RS2 spectroscopic observations of globular clusters (GCs) in five low surface brightness dwarf galaxies: KK 211 and KK 221, both dwarf spheroidal satellites (dSph) of NGC 5128; dSph ...KK 84 located close to the isolated SO galaxy NGC 3115; and two isolated dwarf irregular (dIrr) galaxies, UGC 3755 and ESO 490-17. Our sample is selected from the Sharina et al. database of HST WFPC2 photometry of GC candidates in dwarf galaxies. For objects with accurate radial velocity measurements we confirm 26 as genuine GCs out of the 27 selected candidates from our WFPC2 survey. One candidate appears to be a distant galaxy. Our measurements of the Lick absorption-line indices in the spectra of confirmed GCs and the subsequent comparison with SSP model predictions show that all confirmed GCs in dSphs are old, except GC KK 211-3-149 (6 plus or minus 2 Gyr), which we consider to be the nucleus of KK 211. GCs in UGC 3755 and ESO 490-17 show a spread in ages ranging from t > 1C Gyr to around 1 Gyr. Most of our sample GCs have low metallicities Z/H less than or equal to -1, Two relatively metal-rich clusters with Z/H approximately -0.3 are likely to be associated with NGC 3115. Our sample GCs show in general a complex distribution of alpha -element enhancement with a mean (a/FE) = 0.19 plus or minus 0.04 derived with the x super(2) minimization technique and 0.18 plus or minus 0.12 dex computed with the iterative approach. These values are slightly lower than the mean (a/FE) 0.29 plus or minus 0.01 for typical Milky Way GCs. We compare other abundance ratios with those of Local Group GCs and find indications for systematic differences in N and Ca abundance. The specific frequencies, SN, of our sample galaxies are in line with the predictions of a simple mass-loss model for dwarf galaxies and compare well with SN values found for dwarf galaxies in nearby galaxy clusters.
We present integrated JHK
S Two-Micron All-Sky Survey photometry and a compilation of integrated-light optical photoelectric measurements for 84 star clusters in the Magellanic Clouds. These clusters ...range in age from ≈200 Myr to >10 Gyr, and have Fe/H values from −2.2 to −0.1 dex. We find a spread in the intrinsic colours of clusters with similar ages and metallicities, at least some of which is due to stochastic fluctuations in the number of bright stars residing in low-mass clusters. We use 54 clusters with the most-reliable age and metallicity estimates as test particles to evaluate the performance of four widely used simple stellar population models in the optical/near-infrared (near-IR) colour-colour space. All models reproduce the reddening-corrected colours of the old (≥10 Gyr) globular clusters quite well, but model performance varies at younger ages. In order to account for the effects of stochastic fluctuations in individual clusters, we provide composite B−V, B−J, V−J, V−K
S and J−K
S colours for Magellanic Cloud clusters in several different age intervals. The accumulated masses for most composite clusters are higher than that needed to keep luminosity variations due to stochastic fluctuations below the 10 per cent level. The colours of the composite clusters are clearly distinct in optical-near-IR colour-colour space for the following intervals of age: >10 Gyr, 2-9 Gyr, 1-2 Gyr, and 200 Myr−1 Gyr. This suggests that a combination of optical plus near-IR colours can be used to differentiate clusters of different age and metallicity.
A study of rotating globular clusters Kacharov, N; Bianchini, P; Koch, A ...
Astronomy and astrophysics (Berlin),
07/2014, Letnik:
567
Journal Article
Recenzirano
Odprti dostop
NGC 4372 is a poorly studied old, very metal-poor globular cluster (GC) located in the inner Milky Way halo. We present the first in-depth study of the kinematic properties and derive the structural ...parameters of NGC 4372 based on the fit of a Plummer profile and a rotating, physical model. We explore the link between internal rotation to different cluster properties and together with similar studies of more GCs, we put these in the context of globular cluster formation and evolution. Our results show that NGC 4372 has an unusually high ratio of rotation amplitude to velocity dispersion (1.2 vs. 4.5 km ssup -1) for its metallicity.
ABSTRACT We report the first direct imaging of protoplanetary disks in the star-forming region of Carina, the most distant massive cluster in which disks have been imaged. Using the Atacama Large ...Millimeter/sub-millimeter Array (ALMA), the disks are observed around two young stellar objects (YSOs) that are embedded inside evaporating gaseous globules and exhibit jet activity. The disks have an average radius of 60 au and total masses of 30 and 50 . Given the measured masses, the minimum timescale required for planet formation (∼1-2 Myr) and the average age of the Carina population (∼1-4 Myr), it is plausible that young planets are present or their formation is currently ongoing in these disks. The non-detection of millimeter emission above the 4 threshold ( ) in the core of the massive cluster Trumpler 14, an area containing previously identified proplyd candidates, suggests evidence for rapid photo-evaporative disk destruction in the cluster's harsh radiation field. This would prevent the formation of giant gas planets in disks located in the cores of Carina's dense subclusters, whereas the majority of YSO disks in the wider Carina region remain unaffected by external photoevaporation.
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